/*
 * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
 *
 * Portions are Copyright (C) 1998 Netscape Communications Corporation.
 *
 * Other contributors:
 *   Robert O'Callahan <roc+@cs.cmu.edu>
 *   David Baron <dbaron@fas.harvard.edu>
 *   Christian Biesinger <cbiesinger@web.de>
 *   Randall Jesup <rjesup@wgate.com>
 *   Roland Mainz <roland.mainz@informatik.med.uni-giessen.de>
 *   Josh Soref <timeless@mac.com>
 *   Boris Zbarsky <bzbarsky@mit.edu>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
 *
 * Alternatively, the contents of this file may be used under the terms
 * of either the Mozilla Public License Version 1.1, found at
 * http://www.mozilla.org/MPL/ (the "MPL") or the GNU General Public
 * License Version 2.0, found at http://www.fsf.org/copyleft/gpl.html
 * (the "GPL"), in which case the provisions of the MPL or the GPL are
 * applicable instead of those above.  If you wish to allow use of your
 * version of this file only under the terms of one of those two
 * licenses (the MPL or the GPL) and not to allow others to use your
 * version of this file under the LGPL, indicate your decision by
 * deletingthe provisions above and replace them with the notice and
 * other provisions required by the MPL or the GPL, as the case may be.
 * If you do not delete the provisions above, a recipient may use your
 * version of this file under any of the LGPL, the MPL or the GPL.
 */

#include "flutter/sky/engine/core/rendering/ScrollAlignment.h"

#include "flutter/sky/engine/platform/geometry/LayoutRect.h"

namespace blink {

const ScrollAlignment ScrollAlignment::alignCenterIfNeeded = {
    ScrollAlignmentNoScroll, ScrollAlignmentCenter, ScrollAlignmentClosestEdge};
const ScrollAlignment ScrollAlignment::alignToEdgeIfNeeded = {
    ScrollAlignmentNoScroll, ScrollAlignmentClosestEdge,
    ScrollAlignmentClosestEdge};
const ScrollAlignment ScrollAlignment::alignCenterAlways = {
    ScrollAlignmentCenter, ScrollAlignmentCenter, ScrollAlignmentCenter};
const ScrollAlignment ScrollAlignment::alignTopAlways = {
    ScrollAlignmentTop, ScrollAlignmentTop, ScrollAlignmentTop};

#define MIN_INTERSECT_FOR_REVEAL 32

LayoutRect ScrollAlignment::getRectToExpose(const LayoutRect& visibleRect,
                                            const LayoutRect& exposeRect,
                                            const ScrollAlignment& alignX,
                                            const ScrollAlignment& alignY) {
  // Determine the appropriate X behavior.
  ScrollAlignmentBehavior scrollX;
  LayoutRect exposeRectX(exposeRect.x(), visibleRect.y(), exposeRect.width(),
                         visibleRect.height());
  LayoutUnit intersectWidth = intersection(visibleRect, exposeRectX).width();
  if (intersectWidth == exposeRect.width() ||
      intersectWidth >= MIN_INTERSECT_FOR_REVEAL) {
    // If the rectangle is fully visible, use the specified visible behavior.
    // If the rectangle is partially visible, but over a certain threshold,
    // then treat it as fully visible to avoid unnecessary horizontal scrolling
    scrollX = getVisibleBehavior(alignX);
  } else if (intersectWidth == visibleRect.width()) {
    // If the rect is bigger than the visible area, don't bother trying to
    // center. Other alignments will work.
    scrollX = getVisibleBehavior(alignX);
    if (scrollX == ScrollAlignmentCenter)
      scrollX = ScrollAlignmentNoScroll;
  } else if (intersectWidth > 0) {
    // If the rectangle is partially visible, but not above the minimum
    // threshold, use the specified partial behavior
    scrollX = getPartialBehavior(alignX);
  } else {
    scrollX = getHiddenBehavior(alignX);
  }

  if (scrollX == ScrollAlignmentClosestEdge) {
    // Closest edge is the right in two cases:
    // (1) exposeRect to the right of and smaller than visibleRect
    // (2) exposeRect to the left of and larger than visibleRect
    if ((exposeRect.maxX() > visibleRect.maxX() &&
         exposeRect.width() < visibleRect.width()) ||
        (exposeRect.maxX() < visibleRect.maxX() &&
         exposeRect.width() > visibleRect.width())) {
      scrollX = ScrollAlignmentRight;
    }
  }

  // Given the X behavior, compute the X coordinate.
  LayoutUnit x;
  if (scrollX == ScrollAlignmentNoScroll)
    x = visibleRect.x();
  else if (scrollX == ScrollAlignmentRight)
    x = exposeRect.maxX() - visibleRect.width();
  else if (scrollX == ScrollAlignmentCenter)
    x = exposeRect.x() + (exposeRect.width() - visibleRect.width()) / 2;
  else
    x = exposeRect.x();

  // Determine the appropriate Y behavior.
  ScrollAlignmentBehavior scrollY;
  LayoutRect exposeRectY(visibleRect.x(), exposeRect.y(), visibleRect.width(),
                         exposeRect.height());
  LayoutUnit intersectHeight = intersection(visibleRect, exposeRectY).height();
  if (intersectHeight == exposeRect.height()) {
    // If the rectangle is fully visible, use the specified visible behavior.
    scrollY = getVisibleBehavior(alignY);
  } else if (intersectHeight == visibleRect.height()) {
    // If the rect is bigger than the visible area, don't bother trying to
    // center. Other alignments will work.
    scrollY = getVisibleBehavior(alignY);
    if (scrollY == ScrollAlignmentCenter)
      scrollY = ScrollAlignmentNoScroll;
  } else if (intersectHeight > 0) {
    // If the rectangle is partially visible, use the specified partial behavior
    scrollY = getPartialBehavior(alignY);
  } else {
    scrollY = getHiddenBehavior(alignY);
  }

  if (scrollY == ScrollAlignmentClosestEdge) {
    // Closest edge is the bottom in two cases:
    // (1) exposeRect below and smaller than visibleRect
    // (2) exposeRect above and larger than visibleRect
    if ((exposeRect.maxY() > visibleRect.maxY() &&
         exposeRect.height() < visibleRect.height()) ||
        (exposeRect.maxY() < visibleRect.maxY() &&
         exposeRect.height() > visibleRect.height())) {
      scrollY = ScrollAlignmentBottom;
    }
  }

  // Given the Y behavior, compute the Y coordinate.
  LayoutUnit y;
  if (scrollY == ScrollAlignmentNoScroll)
    y = visibleRect.y();
  else if (scrollY == ScrollAlignmentBottom)
    y = exposeRect.maxY() - visibleRect.height();
  else if (scrollY == ScrollAlignmentCenter)
    y = exposeRect.y() + (exposeRect.height() - visibleRect.height()) / 2;
  else
    y = exposeRect.y();

  return LayoutRect(LayoutPoint(x, y), visibleRect.size());
}

};  // namespace blink
